Apples, Acids, & Bases

Sometimes the best curriculum ideas come not from prior planning, but spontaneously following through on the expressed interests of kids. After making a HUGE mess playing with the ink inside a broken pen, this curious group came to me to plead their case.  With straight faces and genuine sincerity they said, "But Carmen, we were EXPERIMENTING!  We like to experiment."  

So the next day we experimented with ACIDS and BASES.  

First we had to think like scientists.  We had to have a question.  We did a little research online and found an experiment we wanted to try.  We learned from our research that apples and other fruit can turn brown when cut open and enzymes inside of the fruit are exposed to oxygen and react with an iron or copper cofactor in the fruit. The apple oxidizes... so it is a little bit like an edible rust on the fruit.

Our research question: What will keep apples from turning brown, an acid or a base?

Our hypothesis: We thought the apple treated with a base (baking soda specifically) would turn brown first.

Materials:

• 5 apple slices
• 5 canning jars with lids
• Vinegar (or dilute acetic acid)
• Lemon juice
• Water
• Baking soda dissolved in water
• Solution of Milk of Magnesia and water

Procedures:

1. We added a slice of apple to each jar.
2. We poured enough of each liquid into the jar to completely coat the apple slices
3. We put the jars on a white board and labeled each space.
4. Then we made a guess about which one would keep the apples looking the freshest.  
5. We made our hypothesis and wrote it down.  We watched our experiment for 2 days then unveiled our apples!  

Results: Our hypothesis was supported. The apple slices in the acids (lemon juice and vinegar) did not get brown as much as the apple slices in the bases (milk of magnesia and baking soda water) or our control (plain water).

by Carmen Prince-Morris